The present invention relates to a low power consumption precharge type programmable logic array (PLA) having the feature indicated in the preamble clause of claim 1, as disclosed in e.g. JP-A-63 177 615.
Fig. 1 is a diagram showing the configuration of another conventional PLA which is frequently used in the prior art.
This PLA is an asynchronous type or a ratio type.
In the diagram, when a high level input signal (H or 1) is provided to an input line 10 which is one of a plurality of input lines arranged in an AND array plane of the PLA, all the array transistors, each of which comprises an N-channel conductivity type transistor, with the drain terminals connected to the input line 10, enter an ON state or an activated state.
For example, a product term line 11 connected to the power source VDD through a load transistor T11 which comprises a P-channel conductivity type transistor and is in the ON state at all times is connected to ground through the array transistor T10, when the array transistor T10 enters the ON state.
In such a situation, the magnitude of the potential of the product term line 11 is determined in accordance with the rate between the ON resistance of the load transistor T11 and that of the array transistor T10. The channel conductance of the load transistor T11 is smaller than that of the array transistor T10. Accordingly, the potential of the product term line 11 is switched to low level from high level.
When the product term line 11 enters the low level, a plurality of array transistors in an OR array plane connected to the product term lines 11 enter the OFF state.
When the array transistor T12 enters the OFF state, the potential of an output line 12 connected to the power source VDD through a load transistor T13 comprising the P channel conductivity type transistor enters the high level from the low level.
At this time, the other array transistors connected to the output line 12 must be in the OFF state.
Therefore a low level output signal as the reversed potential of the output line 12 is provided to an output terminal OUT1 of the OR array plane.
On the other hand, when a low level input signal is provided to the input line 10 through an input terminal IN1, the operations of the AND and the OR array planes described above are reversed, the electrical potential of the product term line 11 remains at the high level, and the output signal of the high level is provided through the output terminal OUT1.
In the PLA, when the input line 10 is at the high level, the array transistor T10 is ON and a current flows continuously to ground through the transistors T10 and T11 which are in the ON state.
The array transistors other than the array transistor T10 connected to high level input line in the AND array plane are operated similarly.
When the input line is at the low level, an array transistor T12 in the OR array plane remains at the high level and a current flows continuously from the power source VDD to ground through the load transistor T13 and the array transistor T12 which are in the ON state because the product term line 11 is maintained at the high level.
The array transistors for which the gate terminals are connected to the high level product term lines are operated similarly.
Thus, a problem with the conventional PLA in the prior art is that the current flows continuously from the power source VDD to ground through the array and the load transistors when the PLA is activated.
We will explain another problem occurring when the conventional PLA described above is incorporated in a data processing system in the prior art.
Fig. 2 is a block diagram of a data processing system with the conventional PLA.
The data processing system is operated according to the following procedures:
First, instructions written in an machine language stored in the memory 70 are read out by a memory fetch unit 71, then stored in a machine language register 72. At the same time, the instruction fetch unit 72 sets a valid bit register 73a to "1".
The machine language instruction is transferred to a PLA 74, then decoded and set in the micro instruction register 75. At the same time, the contents of the valid bit register 73a are set in a valid bit register 73b. An execution unit 76 implements the data processing operation in accordance with the contents of the micro instruction register 75. These units such as the instruction fetch unit 71, the PLA 74, and the execution unit 76 described above are installed in parallel.
Thus, the steady electrical current flows continuously in the conventional PLA and the data processing system using the conventional PLA when the power source is turned on.
Namely, the electric current flows in the conventional PLA when the power source is turned on and no effective output is provided (hereinafter referred to as the unused state). The power consumption of the PLA or the data processing system in the situation described above is increased by the steady electrical current flowing therein.
The larger the scale of the PLA and the greater the number of the array transistors, the more power consumed when the PLA is in the unused state.
Moreover, the power consumption of the PLA is increased when it is in the unused state for a long time. In the data processing system with the conventional PLA, no effective output of the PLA 74 can be provided when no machine language instruction is stored in the machine language register 72 and when the content of the valid bit register 73a are zero.
The power consumption of the PLA is increased because the PLA 74 is in operation when the content of the valid bit register 73a are zero.
When effective data is stored in the micro instruction register 75 (the content of the valid bit register 73b are 1) and the execution unit 76 is executing, the contents of the micro instruction register 75 cannot be stored until the operation of the execution unit 76 is finished. Specially, even if an effective output is provided from the PLA 74, it cannot be stored in the micro instruction register 75.
Accordingly, the operation of the PLA 74 has no meaning while the valid bit register 73b is set at 1 and the execution unit 76 is executing. Thus, the power consumption of the PLA 74 is increased.
An object of the present invention is to provide a low power consumption precharge type programmable logic array (PLA) which is capable of reducing the power consumption while the PLA is in the unused state and a data processing system incorporating the PLA.
The PLA according to the present invention has the features indicated in claim 1 or claim 2. A preferred embodiment of the invention is indicated in claim 3.
Accordingly, the power consumption of the PLA according to the present invention can be reduced.
Moreover, the PLA described above can be applied to various data processing system.
These and other objects, features and advantages of the present invention will be more apparent from the following description of a preferred embodiment, taken in conjunction with the accompanying drawing.
Preferred embodiments according to the present invention will now be explained referring to the drawings.
Next, we will explain an embodiment according to the present invention, in which this invention is applied to a precharge type programmable logic array.
Fig. 3 is a brief configuration diagram of a precharge type programmable logic array according to the present invention.
In an AND plane of the same diagram, the enable signal and the inverted signal of a clock signal CLOCK1 are provided to the input terminals of the NAND gate G30, then the output of the NAND gate G30 is provided to the gate of the precharge transistor P11 which keeps the product term lines 11 at a predetermined potential level.
In an OR plane, the output of the product term line 11 in the AND plane is provided to the product term lines in the OR plane through the AND gate G32.
The enable signal and the inverted signal of the clock signal CLOCK2 are provided to the input terminals of the NAND gate G31, then the signal from the NAND gate 31 is provided to one of the input terminals of the AND gate 32.
The output of the product term line in the AND plane is supplied to the other input terminal of the AND gate G32.
The phase of the clock signal CLOCK1 differs from that of the clock signal CLOCK2.
In the PLA according to the present embodiment, the PLA operates normally (namely, it enters the active state) during the time period between the times t3 and t4 as shown in Fig. 3 when the enable signal EN is in the high level. The end timing of the precharge operation in the PLA is detected at the time t3 which is a rising portion of the clock signal CLOCK2.
On the other hand, the PLA cannot operate (namely, it enters the inactive state) during the time period between the times t1 and t3 as shown in Fig. 3 when the enable signal EN is in the low level.
In the prior art, the precharge operation for the PLA is continuously executed in the activate state of the PLA.
On the other hand, the PLA of the present embodiment can also decrease its power consumption while the enable signal EN is in the low state.
The preferred timing period between the time t2 and the time t3 may be determined in accordance with the kind of the PLA.
Various modification will become possible for those skilled in the art after the teaching of the present disclosure without departing from the scope as defined in the annexed claims.
Reference signs in the claims are intended for better understanding and shall not limit the scope of the claims.